The 51s committed four errors last night, three of which came in the fifth inning with one of the three coming on a throwing error by Montero.
Montero was relieved by Justin Hampson, who earned the win in the 51s 11-5 victory over Colorado Springs.
It was Montero's second start for Las Vegas this season - he made a spot start at Triple-A last month before returning to Double-A Binghamton.
Overall, Montero is 7-4 with a 2.40 ERA in 13 starts between Double-A Binghamton and Triple-A Las Vegas in 2013.
During a Q&A session at Citi Field yesterday, Sandy Alderson said due to Montero not being on the 40-man roster, it was unlikely he would make his big league debut this season.